1. Field of the Invention
The present invention relates to an antenna device used for a contactless Integrated Circuit (IC) tag which uses Radio Frequency Identification (RFID) technology, and a method of manufacturing the same.
2. Description of the Related Art
Recently, RFID systems, such as contactless IC cards, have come into wide use. The RFID systems contactlessly receive power and information from an external device, such as a reader/writer, by using radio waves, and contactlessly transmit the information to another external device. Such RFID systems include an antenna device for reception/transmission of signals, and an IC chip, and are configured to be capable of wirelessly communicating with an external device.
If an antenna device employed in such an RFID system is positioned adjacent to metal, magnetic flux is converted into over-current in the metal, which makes it impossible to execute communication. As a countermeasure to this, it has been proposed to provide a planar antenna and to attach a radio wave absorbent to the planar antenna.
FIG. 1 is a cross-sectional view showing a conventional antenna device with a planar antenna provided with a radio wave absorbent. As shown in FIG. 1, the conventional antenna device includes a radio wave absorbent 106 attached to the bottom side of a loop antenna 104 with a double side adhesive tape 105. The loop antenna 104 includes an antenna pattern 102 formed on a polyimide (PI) film 101, and an insulating passivation layer 103 formed on the PI film 101 to cover the antenna pattern 102. The antenna pattern 102 is formed by depositing a conductor (e.g. a. metallic conductor, such as copper) layer on the top side of the PI film 101, and then etching the conductor layer through a conventional lithographic process.
Since such a conventional construction has a limit in thinning, it is difficult to satisfy the recent demand of miniaturizing and slimming electronic appliances.
In addition, the individual components of the antenna device, for example, a loop antenna, a double side adhesive tape, and a radio wave absorbent should be manufactured through independent processes, respectively, and then the radio wave absorbent should be attached to the loop antenna with the double side adhesive tape. Consequently, there is a problem in that the manufacturing process of such an antenna device is complicated, and the manufacturing cost is high.